This invention relates to the control of machine tools, and more particularly to a method of controlling programmed movements effected by a plurality of actuators actuating one or more moving parts of a machine tool so as to carry out a machining operation on a rough workpiece fixed to a workpiece holder of this machine tool. The invention further relates to a device for controlling one or more axes in a machine tool, of the type having a driving motor on each axis and, for all the axes, a numerical data memory and a program capable of distributing a series of movement orders to each motor.
Conventional machine tools of the mechanical type, e.g., automatic lathes, are known to comprise cams, i.e., mechanical parts containing the program for machining the workpieces. Each cam communicates a movement to the tool by a description of the evolute of its profile. The connection between the feeler and the cam is continuously maintained so that the position of the tool is at all times a function of the radius of the cam at the location where it is in contact with the feeler. Such a control may be likened to an open-loop control.
In recent years, besides these conventional machines, so-called NC (numerically controlled) machines have been developed. The various "axes" of the machine are actuated by actuators. The program calculates a sequence of instructions which are transmitted to regulators, and the motors of the different axes are controlled by these regulators. The control is of the closed-loop type. A sensor gives the position of the axis at all times, so that a comparison can be made between the reference value and the actual value. The deviation determines an adjustment movement.